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MONTGOMERY. 
[Vol. XV. 
are first produced, but a varying number are formed simultane¬ 
ously and at different parts of the cell; it is usually, though 
not always, the case that they first arise at the periphery of the 
cell at some distance from the nucleus. The mature yolk 
globules are slightly larger than these and stain somewhat 
more intensely, which shows that they gradually become denser 
as they increase in size ; in the largest ova these spherules 
are so abundant that the true cytoplasm is quite obscured 
(Fig. 247). 
First nucleolar stage. — In the smallest nuclei found there is 
a peripheral group of several nucleoli lying close to the nuclear 
membrane, which are spherical in form (Figs. 236-238). 
Second nucleolar stage. —The nucleoli have increased in num¬ 
ber, and, departing from their original peripheral position, now 
occupy the center of the nucleus (Figs. 239 and 240). So small 
are they, and so densely grouped may they become, that at 
first sight one might be led to suppose that each group of 
numerous nucleoli was a single nucleolus. In those cases 
where the nucleus is oval or elongated in form, instead of 
spherical (the usual case), in the place of a single cluster two 
are commonly present, or else the single mass or cluster of 
nucleoli is elongate in shape, its outline being more or less par¬ 
allel to the contour of the nucleus. The nucleoli in this stage 
are always more numerous and usually also smaller than those 
of the previous period ; their increase in number might thus 
be brought about, in part at least, by divisions of the earlier 
nucleoli. 
Third nucleolar stage. —The nucleus now is much larger, 
and the nucleoli begin to wander apart towards the periphery 
of the nucleus (Figs. 241, 243, 246, 247). I have observed all 
stages between nuclei containing centrally grouped, small 
nucleoli and those in which they have come to lie close to the 
nuclear membrane. In this stage, as in the preceding one, 
the nucleoli are perfectly homogeneous without vacuoles, and 
spherical in form. In a few nuclei, however, they appear 
greatly vacuolated, but these cases are so rare that they must 
be considered abnormal. At the end of this period they attain 
their greatest dimensions, though they thereby become some- 
